In recent years, there has been a strong demand for fuel-efficient automotive tires out of concern for the environment and resources and there has been a further demand for superior wet-grip properties and strength out of concern for safety. A tire made from a rubber composition containing silica as a filler is better in low-heat-generating properties and can therefore make a more fuel-efficient tire than a tire made from a rubber composition containing conventionally-used carbon black.
As a conjugated diene rubber that is used for providing such a fuel-efficient tire, Patent Literature 1 discloses a conjugated diene rubber that is obtained by causing a particular halogenated tin compound to react with a conjugated diene polymer chain having an isoprene block at one end thereof and an active terminal at the other end. Further, Patent Literature 2 discloses a conjugated diene rubber containing a predetermined amount or more of a structure formed by binding of three or more conjugated diene polymer chains produced by causing a particular denaturant to react with a conjugated diene polymer chain having an isoprene block at one end thereof and an active terminal at the other end.